1. Field of the Invention
The invention relates to a regulator used for controlling an alternator of a motor vehicle.
2. Description of the Prior Art
In a motor vehicle a regulator is used in combination with an alternator to monitor and maintain the system voltage by varying the alternators output current. The regulator does this by varying the rotor""s field current which controls the alternator""s output current. Thus the output current of the alternator is a function of the rotor field current. For this reason, if the system voltage decreases too low for any reason, then the current in the rotor""s field will decrease reducing the alternators maximum current. When an alternator is running at a low RPM and high output current the temperature of the windings increases due to low air flow and high resistance losses. This increase in temperature raises the resistance of the field further decreasing the maximum alternator output. If the alternator""s maximum current falls below the system requirements then the battery well will discharge to the point where the engine quits running. This is a common scenario with specialty vehicles such as buses, firetrucks, ambulances, limousines, and police cars that have large electrical loads and frequently operate at low engine RPM while parked.
It is an object of the invention to provide a capacitor-diode arrangement in a regulator to boost the regulator output to the rotor field coil of the alternator and hence the output of the alternator when needed. The invention is termed xe2x80x9cField Current Droop Compensationxe2x80x9d or xe2x80x9cFCDCxe2x80x9d as it will be referred to hereinafter. The increased output voltage to the rotor""s field coil that FCDC provides will add approximately 20% increase to the output current capability of any alternator. This increased output is used to compensate for normal operating factors that reduce the field current thus limiting the maximum output of the alternator. The maximum output current of an alternator is a function of field current, temperature, RPM and other factors. When an alternator is operating at low RPM and high output current the temperature of the windings increases dramatically due to the low volume of air flow and high resistive losses. This temperature increase raises the resistance of the rotor""s field coil windings which decreases the current through the field and the maximum output current of the alternator. When the charging system is under heavy load due to deeply depleted batteries and/or high system demands, the system voltage decreases as a result. This decrease in system voltage further reduces the current in the rotor""s field and the maximum alternator output. This can lead to a runaway discharge condition if the maximum alternator output falls below system demands. Eventually the battery will discharge to the point where the engine quits running. FCDC increases the voltage and current available to the rotor""s field to help prevent the runaway discharge condition. This system is not limited to any particular alternator or charging system. It can be used with any alternator based charging system or various systems of different voltages.
The regulator includes a control circuit for controlling a control switch. The control switch has an output coupled to a field terminal which is to be coupled to the rotor""s field coil. The regulator also includes a stator terminal coupled to the control circuit, an ignition terminal coupled to the control circuit for turning the regulator on and off; and a positive battery terminal coupled to the control circuit. The capacitor-diode arrangement comprises a capacitor means coupled between the stator terminal and the input of the control switch. The diode has an anode coupled to the battery terminal and a cathode coupled to the input of the switch.